Thermostatic switch



1951 F. M. GATES ET AL 2,538,512

THERMOSTATIC SWITCH Filed Nov. 7, 1947 i v E 1 ii I i Y5 1%;

' INVENTQRS FRANKUN M .GATES Y HERBERTJLCOURTNEY 1!. MM

ATTORNEY Patented Jan. 16, 1951 UNITED STATES PATENT OFFICE THERMOSTATIC SWITCH Franklin M. Gates, West Hartford, and Herbert W. Courtney, Farmington, Conn., assignors to The Smith Gates Corporation, Plainville, Conn., a corporation of Connecticut Application November 7, 1947, Serial No. 784,722 11 Claims. (Cl. 200-139) The invention relates to a switch adapted to be automatically opened or closed in accordance with changes in the temperature. A switch embodying the invention is particularly adapted for use in conjunction with a heating unit, which is started when the temperature falls below a predetermined critical temperature so as to close the switch and which is'stopped when the temperature rises above the said critical temperature so as to open the switch. While not necessarily so limited, 9. switch embodying the invention is particularly adapted for use in or as a part of an immersion water heater.

The general object of the invention is to provide a switch of the type described which is compact, simple and inexpensive, and which is dependable and issensitive to very small temperature changes.

A specific object of the invention is to provide simple thermostatically controlled toggle means for moving the movable contact of the switch to its on and "011? positions with a snap action.

Another specific object of the invention is to provide a simple and efiective stop for positively limiting the extent of movement of the bimetallic element forming a part of the switch.

A still further specific object of the invention is to provide an advantageous relationship between the bimetallicelement and the other parts of the switch. The mounting and relationship of the bimetallic element is particularly useful when the switch is incorporated in an immersion water heater.

A still further object of the invention is to provide a simple and effective means for adjusting the bimetallic element to change the beforementloned critical temperature.

Other objects of the invention will be apparent from the drawing and from the following specification and claims.

In the drawing we have shown in detail a preferred embodiment of the invention, but it will be understood that various changes may be made from the construction shown, and that the drawings are not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose.

Of the drawing. i

Fig. 1 is-a plan view of a switch embodying the invention, the movable contact being shown in its "on position.

Fig. 2 is a view similar to Fig. 1, but with the movable contact shown in its "ofi position,

Fig. 3 is a vertical sectional view taken alon the line 3-3 of Fig. 1.

Fig. 4 is a side view.

Fig. 5 is a detail view of the flexible strip which carries the movable contact.

Fig. 6 is a fragmentary vertical sectional view taken along the line 8-6 of Fig. 1.

A switch embodying the invention is particularly adapted to be of relatively small size. It is shown in the drawing on a comparatively large scale for the sake of clarity.

Referring to the drawing, Ill represents an insulating base on which all of the other parts of the switch are mounted. As shown, the base is a circular disc with a depending annular flange. For convenience of description it will be assumed that the switch is positioned with the base horizontal, but the invention is notso limited and the switch may be variously positioned.

Secured to the base near one side thereof is a support l2, comprising a metallic bar which is perpendicular to the base and which has an angle portion secured to the base by means of a rivet l4 extending therethrough. Rigidly or fixedly secured to the support l2, as for instance by means of a rivet I6, is a thin resilient metallic strip H3. The strip I8 is perpendicular to the base and it extends from the said support l2 parallelly with the base and preferably approximately across the center thereof. Secured to the strip l8 near the end thereof opposite the said support I2 is an electrical contact 20 which is preferably in the form of a round button having a convex contact face.

Secured to the base. near the opposite side thereof is a support 22, comprising a metallic bar which is perpendicular to the base and which has an angle portion secured to the base by means of a rivet 24 extending therethrough. Carried by the support 22 is a stationary electrical contact 26 positioned to be engaged by the movable electrical contact 20.

Connected with the rivets I4 and 24 which hold the supports I2 and 22 are wire terminals 28 and 30 which may be of any usual or preferred form. It will be seen that when the movable contact 20 is engaged with the stationary contact 26, as shown in Fig. 1, an electrical circuit isestablished through the switch between the said wire terminals.

The resilient strip It has a, longitudinally extending opening therein which is entirely surrounded by integral portions of the strip. As shown, the longitudinally extending opening includes parallel longitudinal slots 34 and 36 and also includes a transverse portion 88 extending between the said longitudinal slots. A longitudinal bow spring 32 is provided which is connected with the strip l-I at that end of the opening therein which is adjacent the movable contact. The bow spring may be fjm'med integrally with the metaLof the strip l8 and it is O" ShOW n. When formed integrally, the bow spring is initially inthe same plane as the main body of the strip.

A toggle member 48 is provided which is supported entirely by the strip l8. Preferably the 88k member 48 is formed of insulating material, and is a flat plate parallel with the front of the base i8. One end of the toggle member is notched and is pivotally engaged at 42 with the metal of the strip It at the end of the opening therein remote from the contacts, and the other end of the toggle member is notched and is pivotally engaged at 44 with the adjacent end of the bow spring 32. The length of the toggle member between the pivotal connections 42 and 44 is such that the spring 32 is bowed as shown in Figs. 1 and 2 when the toggle member is in place. The axes of pivotal movement at 42 and 44 are perpendicular to the base l8, and the axis at 42 is in the plane of the strip l8. By reason of the pivotal connections at 42 and 44, a toggle action is provided by the toggle member 48 and by the bow spring 38. When the toggle member is in the position shown in Fig. 1, the bow spring holds the movable contact 28 in engagement with the stationary contact, 28. When the toggle member is in the position shown in Fig. 2, the bow spring holds the movable contact 28 out of engagement with the stationary contact 28.

In order that the toggle mefnber 48 may be more effectively supported by the strip l8 and by the bow spring 32, projections 43, 48 are provided at the ends of the pivotal edge 42 on the strip i8 and projections 48, 48 are provided at the ends of the pivotal edge 44 on the spring 82. These projections are at opposite sides of the toggle member 48 as shown in Fig. 3 and they assist in supporting it and in holding it in place.

The portion of the toggle member 48 eflectlve for toggle action is that between the axes 42 and 44. In order that the toggle member 48 may be operated it has a relatively large extension 4| at one side as clearly shown in Figs. 1 and 2.

For pivotally moving the toggle member 48 about its pivotal axis at 42 in accordance with changes in temperature, there is provided a bimetallic element 48. The position and shape of the bimetallic element 48 may be widely varied, but I preferably provide a bimetallic element comprising a strip which is circularly curved to substantially conform to a hypothetical geometric cylinder perpendicular to the base. Preferably and as shown, the hypothetical geometric cylinder to which the strip 48 substantially conforms is concentric with the circular base l8, but has a somewhat smaller diameter. The flexible strip II, the contacts 28 and 28, the bow spring 82 and the toggle member 48 are all within the said geometric cylinder.

The bimetallic stri 48 is so constituted that it tends to deflect outward to increase the radius of curvature when the temperature increases, and that it tends to deflect inward to decrease the radius of curvature when the temperature decreases. For supporting the bimetallic strip 48 on the base there is provided an arm 48 having a portion 88 which extends away from the base and perpendicularly thereto. The bimetallic element 48 is secured to the said portion 88 by suitable means, as for instance by a rivet 82. The bimetallic strip 48 is provided near its opposite end with a hole through which extends a Pin 84 which is carried by the toggle member and which is parallel with the base l8.

It may be assumed that when the parts are in the positions shown in Fig. l, the ambient temperature is slightly below a predetermined critical temperature. With the parts in the said positions, the axis of connection at 44 between the bow spring 32 and the toggle member 48 is at the side of the strip II which is opposite the stationary contact 28. The result is that the bow spring 32 flexes the strip 18 in the direction to hold the movable contact 28 in engagement with the stationary contact 28. If the switch is in the control circuit of a heating unit, the said unit is operated to increase the ambient temperature. As the temperature increases to a point slightly above the said critical temperature, the radius of curvature of the bimetallic element 48 is increased and the toggle member 48 is swung in the counterclockwise direction about the axis at 42. As soon as this movement of the toggle member 48 carries the axis at 44 to the other side of the resilient strip iii, the bow spring 82 acts to flex the strip is in the opposite direction so as to separate the movable contact 28 from the stationary contact 28, as shown in Fig. 2. Preferably, a pin 58 is carried by the base adjacent the movable end of the resilient strip l8. This pin is in position to engage the back of the contact button 28 to limit movement of the contact in the 011" direction.

With the switch in the .ofl position shown in Fig. 2 the heating unit is not operated and there is a tendency for the temperature to decrease. As the temperature decreases to a point slightly below the critical temperature, the toggle member 48 is swung in the clockwise direction to restore the axis at 44 to a position at or near that shown in Fig. 1, whereupon the bow spring 82 acts to again flex the resilient strip l8 and to return the movable contact 28 to its position oi engagement with the stationary contact 28 as shown in Fig. 1.

The toggle member 48 moves very slowly in each direction in accordance with the movement 01' the bimetallic strip in response to changes in temperature. However, as the axis at 44 moves from one side of the strip is to the other, the movable contact is moved quickly with a snap action either to its 011" position as shown in Fig. 2, or to its "on position as shown in Fig. l.

A suitable means is preferably provided for limiting the extent of deflection of the bimetallic element 48, such limitation being preferably effected by limiting the extent of angular movement of the toggle member 48. As shown the said member 48 is provided with a hole 88 which is perpendicular to the base. Secured to the base within the aforesaid geometric, cylinder is a pin 88 which extends into the hole 88, the said pin having a diameter somewhat smaller than that of the hole. The relationship between the diameter of the pin 88 and the diameter of the hole 88 is such that there is no engagement during normal operation of the switch, that is; when the bimetallic strip is deflected only within normal predetermined limits. This will be apparent from an inspection of Figs. 1 and 2. However, when the switch is not in use it may be subjected to temperatures much greater or much less than the critical temperature, the result being that the bimetallic element may tend to deflect outward or inward to extents far greater than the extents necessary for operating the toggle member. Any excessive deflection of the bimetallic element and any excessive movement of the tog gle member are prevented by the engagement of the stationary pin 60 with the side of the hole 58.

The pin 60 positively prevents movement of the center of curvaturrThe before-mentioned am It is connected with the base III by means of a rivet 62, the said ann being pivotally movable about the said rivet. The axis 01' the rivet is at the center of the base and is therefore at or approximately at the center of curvature of the bimetallic element. For adjusting the arm 48 about the axis of the rivet 62 there is provided a-member 64 which extends through an aperture in thebase and which can be turned therein. The member 64 has an eccentric head" which is entered in a longitudinal slot 68 in the arm #8. The head 05 has a screwdriver slot therein, and by means of a screwdriver inserted in the said slot the said member 64 may be turned to angularly adjust the arm 48 and the bimetallic element 46 in either direction. The member 84 frictionally engages the base so that it will remain in any position to which it may be moved. When the arm and the bimetallic element are moved in the clockwise direction, the critical temperature is increased and when they are moved in the counterclockwise direction the critical temperature is decreased.

' As already stated, a switch embodying the invention is particularly adapted for use in, or as a part of, an immersion water heater. When so used the switch is enclosed within the same casing as the heating unit of the heater. The drawing shows a portion of an enclosing casing Ill. The said casing is indicated by dot-and-dash lines and the showing thereof is intended to be merely diagrammatic. The casing does notof itself constitute any part of the present inven tion. 1

When the switch is enclosed in a casing such as HI the bimetallic element 05 is, throughoutits I entire length, closely adjacent the inner walLgf thecasing. The casing is immersed in the water to be heated, and thus the bimetallic ele-' ment is in position to respond readily and quickly to changes in temperature transmitted through strip being fixedly supported at one end, a movable contact carried by the strip near the opposite end thereof, a stationary contact positioned to be engaged and disengaged by the movable contact, a longitudinal bow spring connected with 6 the strip at that end of the opening therein which is adjacent the movable contact, a toggle member entered in the opening in the strip and entirely supported by the said strip, the said toggle member being pivotally engaged at one end thereof with themetal of the strip at the end of the opening remote from the contacts and being pivotally engaged at its opposite end with the adjacent end of the bow spring, and a bimetallic element operatively connected with the toggle member and serving upon changes in temperature above or below a predetermined critical temperature to pivotally move the said member so that-the line of engagement between the said member and the end of the bow spring is shifted between positions at'opposite sides of the strip and so that the'bow spring is thus enabled to flexthe resilient member and move the movable contact with snap action into or out of engagement with the stationary contact in accordance with movements of the toggle member by the bimetallic element. v

2. A thermostatic snap switch as set forth in' claim 1 wherein the bow spring is formed as an integral part of the resilient metallic strip. I,

3. In a thermostatic switch, the combination'of a resilient metallic strip rigidly supported at one end, a. movable contact on the strip near the,

opposite end thereof, a stationary contact positioned to be engaged by the movable contact; a bimetallic element rigidly supported at one end, means connected with the bimetallic element adjacent the opposite end thereof for flexing the resilient strip to move the movable contact into or out of engagement with the stationary contact as the bimetallic element is deflected within normal predetermined limits in accordance with temperature changes within a narrow range, and stationary means for positively preventing deflection of the bimetallic strip beyond wider predetermined limits outside of the said normal predetermined limits when the said strip is subjected to temperatures outside of the said normal range.

,4. In a thermostatic switch, the combination of a resilient metallic strip fixedly supported at one end, a movable contact on the strip nearthe opposite end thereof, a stationary contact positioned to be engaged by the movable contact, a bow spring connected at one end with thestrip and having a free portion extending longitudinally toward the flxed end thereof, a toggle member mounted for pivotal movement about a trans verse axis parallel-with and adjacent the strip, the said member having pivotal engagement with the free end of the spring so that the spring is bowedand so that a toggle action isprovided-by the saidmember and the said spring, a bimetallic element connectedwith the toggle member and serving upon changes in temperature above or below a predetermined critical temperature to pivotally move the said memberwithin normal predetermined limits so that the line of engagement between the member and the bow spring is shifted between positions at opposite sides of the strip and so that the bow spring is thus enabled to flex the strip and move the movable contact with a snap action into or out of engagement with the stationary contact in accordance with movements of the toggle member by the bimetallic element, and stationary means positioned to be engaged by the toggle member upon movement thereof beyond the said normal predetermined limits, the last said means positively preventing movements of the toggle member beyond wider predetermined limits outside'of the said normal predetermined limits.

5. In a thermostatic switch, the combination of a resilient metallic strip fixedly supported at one end, a movable contact on the strip near the opposite end thereof, a stationary contact positioned to be engaged by the movable contact, a bow spring connected at one end with the strip and having a free portion extending longitudinally toward the fixed end thereof, a toggle member mounted for pivotal movement about a transverse axis parallel with and adjacent the strip, the said member having pivotal engagement with the free end of the spring so that the spring is bowed and so that a toggle action is provided by the said member and the said spring and the said member having a transverse hole therein, a bimetallic element connected with the toggle member and serving upon changes in temperature above or below a predetermined critical temperature to pivotally move the said member within normal predetermined limits so that the line of engagement between the member and the bow spring is shifted between positions at opposite sides of the strip and so that the bow spring is thus enabled to flex the strip and move the movable contact with a snap action into .or out of engagement with the stationary contact in accordance with movements of the toggle member by the bimetallic element, and a stationary pin extending into the hole in the toggle member and serving to positively prevent movements of thetoggle member beyond wider predetermined limits outside of the said normal predetermined limits.

6. In a thermostatic switch, the combination of an insulating base, a bimetallic strip perpendicular to the base and circularly curved to substantially conform to the major portion of a geometric cylinder, means engaging the strip at one end to rigidly support it at the said end so that the remaining portion of the said strip is free and is adapted to deflect in accordance with temperature changes, a resilient metallic strip perpndicular to the base and located entirely within the said cylinder to which the bimetallic strip substantially conforms, the said strip being fixedly connected at one end with the base, a movable contact on the resilient strip near the opposite end thereof, a stationary contact on the base and positioned within the said cylinder for engagement by the said movable contact, and means within the said cylinder and connected with the freeportion of the bimetallic strip for flexing the resilient strip to move the movable contact into or out of engagement with the stationary contact as the bimetallic strip is deflected in accordance with temperature changes.

7. A thermostatic switch as set forth in claim 6 wherein there is a means within the said cylinder for positively preventing deflection of the bimetallic strip beyond predetermined limits.

8. In a thermostatic switch, the combination of a circular insulating base, a bimetallic strip perpendicular to the base and circularly curvid to substantially conform to the major portion of a geometric cylinder having a diameter slightly less than that of the base so that the strip may be closely adjacent a cylindrical casing surrounding and fitting the base, means engaging the strip at one end to rigidly support it at the said end so that the remaining portion of the said strip is free and is adapted to deflect in accordance with temperature changes, a resilient metallic strip perpendicular to the base and lo- 8 cated entirely within the said cylinder to which the bimetallic strip substantially conforms, the said strip being fixedly connected at one end with the base, a movable contact on the resilient strip near the opposite end thereof, a stationary contact on the base positioned within the said geometric cylinder, means engaging the strip at one end to rigidly support it at the said end so that the remaining portion of the said strip is free and is adapted to deflect in accordance with temperature changts, the said strip supporting means being connected with the base for pivotal movement about the axis of the said cylinder to which the bimetallic strip substantially conforms, a resilient metallic strip perpendicular to the base and located entirely within the said cylinder, the said strip being fixedly connected at one end with the base, a movable contact on the resilient strip near the opposite end thereof, a stationary contact on the base positioned within the said cylinder for engagement by the movable contact, means within the said dicular to the base and circularly curved to substantially conform to the major portion of a geometric cylinder, means engaging the strip at one and to rigidly support it at the said end so that the remaining portion of the said strip is free and is adapted to deflect in accordance with temperature changes, a resilient metallic strip perpendicular to the base and located entirely within the cylinder to which thebimetallic strip substantially conforma'the said strip being fixedly connected at one end with the base, a movable contact on th resilient strip near the opposite end thereof, a stationary contact on the base positioned within the said cylinder for engagement by the movable contact, a bow spring connected at one end with the resilient strip near the contact carrying end thereof and extending longitudinally toward the fixed end of the said strip, a toggle member within the said cylinder mounted for pivotal movement about an axis perpendicular to the base and adjacent the fixed end of the resilient strip, the said member having pivotal engagement with the adjacent end of the bow spring so that the spring is bowed and so that a toggle action is provided by the said member and the said spring, and means connecting the free portion of the bimetallic strip with the toggle member to move the toggle member as the bimetallic strip is deflected in accordance with ma am temperature changes above and below a predetermined critical temperature, the said toggle member upon being so moved causing the axis of connection between the toggle member and the bow spring to shiit between positions at opposite sides of the resilient strip with the result HERBERT w. COURTNEY.

nmnncns crrsn The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,289,617 Berry Dec. 31, 1918 1,997,604 Stewart Apr. 16, 1935 2,135,864 Weber Nov. 8, 1938 2,175,721 Taylor Oct. 10, 1939 2,204,949 Riche June 18, 1940 2,235,338 Shaw Mar. 18, 1941 2,298,823 Crum Oct. 13, 1942 

